The present invention relates to a system utilizing and/or controlling a plurality of magnetrons that are powered by a single power supply.
Microwave heating is a technique that can be applied with great advantage in a multiple of processes which include the supply of thermal energy. One advantage is that the heating power can be controlled in the absence of any inertia.
One drawback, however, is that microwave equipment is often more expensive than conventional alternatives. A magnetron of such heating equipment may be driven by a power unit with associated control system, which constitute the major cost of the equipment. Since the output power of the magnetron is limited, heating equipment may require the presence of a significant number of magnetrons and associated power units and control systems to achieve a given heating requirement.
Magnetrons may be used to generate radio frequency (RF) energy. This RF energy may be used for different purposes such as heating items (i.e., microwave heating) or it may be used to generate a plasma. The plasma, in turn, may be used in many different processes, such as thin film deposition, diamond deposition and semiconductor fabrication processes. The RF energy may also be used to create a plasma inside a quartz envelope that generates UV (or visible) light. Those properties decisive in this regard are the high efficiency achieved in converting d.c. power to RF energy and the geometry of the magnetron. One drawback is that the voltage required to produce a given power output varies from magnetron to magnetron. This voltage may be determined predominantly by the internal geometry of the magnetron and the magnetic field strength in the cavity.
Some applications may require two magnetrons to provide the required RF energy. In these situations, an individual power source has been required for each magnetron. Two or more magnetrons may be coupled to a power supply in parallel. However, two magnetrons of identical design may not have identical voltage versus current characteristics. Normal manufacturing tolerance and temperature differences between two identical magnetrons may yield different voltage versus current characteristics. As such, each magnetron may have a slightly different voltage. For example, the magnetrons may have mutually different operating curves such that one magnetron may produce a higher power output than the other magnetron. The magnetron having the higher output power may become hotter than the other, wherewith the operating curve falls and the power supply will be clamped or limited to a lower output voltage. This may cause the power output of the magnetron producing the higher output to fall further until only one magnetron produces all the power due to the failure to reach the knee voltage of the other magnetron. It is desirable to utilize a plurality of magnetrons without these problems.
To achieve these and other objects, embodiments of the present invention may provide a system that includes a power supply device to supply a current, a first magnetron device to be powered by the power supply device, a second magnetron device to be powered by the power supply device and a control circuit to control an amount of current reaching the first magnetron device.
The control circuit may control an amount of current reaching the first magnetron device and an amount of current reaching the second magnetron device.
The control circuit may include a hall effect current transformer coupled between the power supply device and each of the first magnetron device and the second magnetron device. The hall effect current transformer may sense current through two signal lines and adjust a current to at least the first magnetron device such that the first magnetron device and the second magnetron device both receive substantially equal current.
The control circuit may further include a first electromagnet associated with the first magnetron device. The first electromagnet may operate in conjunction with the hall effect current transformer to adjust the current reaching the first magnetron device. The control circuit may also include a second electromagnet associated with the second magnetron device.
The control circuit may include an error amplifier coupled between the hall effect current transformer and the first electromagnet. The control circuit may also include a coil driver device coupled between the hall effect current transformer and the first electromagnet.
Other objects, advantages and salient features of the invention will become apparent from the detailed description taken in conjunction with the annexed drawings, which disclose preferred embodiments of the invention.